The thermal diffusivity of silicon nitride/silicon carbide nanocomposites using a photothermal deflection technique

Measurements are presented to show the effect of mass fraction on thermal d iffusivity of composites fabricated from 200 nm silicon carbide particles d ispersed in a matrix of silicon nitride. The mean composite thermal diffusi vity is measured over a mass fraction range of 0.05 to 0.30 using a phototh ermal deflection technique which creates a frequency-dependent thermal pene tration depth in the material that can be used to reveal local inhomogeneit ies of thermal diffusivity. The results show that a maximum thermal diffusi vity occurs at a mass fraction of 0.10. This peak value follows extrema in fracture toughness and creep rate at this particle loading that had been ob served in prior studies of similarly fabricated nanocomposites. The results are discussed in terms of the competing influences of large thermal diffus ivity of silicon carbide relative to silicon nitride, and the role of inter faces as volume fraction is changed due to the high surface-to-volume ratio of the nanosize particles. The measurements are compared with literature v alues and the trends are explained in terms of the differing particle sizes and binders used in the composites.